Study of Stoichiometry of Ferric Thiocyanate Complex for Analytical Purposes Including F- - Determination

الملخص

The rather old and well known Fe(III)-thiocyanate system has been restudied. The
stepwise mole ratio complexation between them has been carefully confirmed. A
wavelength shift from 460 t0 480 nm has been observed by increasing SCN- ion
concentration and remained constant at 480nm.where Fe(III): SCN- was 1:6. An
improvement in the problem of stability of the complex has also been achieved by
creating an oxidizing medium using 9.5x10-4 M KMnO4 , to prevent the inner redox
reaction between SCN- and CNS-. The stability has been improved from zero time to
about 47 mins. Total iron has been determined in water and drugs down to 0.06ppm Fe3+
with r2 = 0.9997 ,recovery of 99.1-102% and precision of 0.13%. A hypsochromic
shift from 480 to 410 nm. caused by the effect of fluoride ion was exploited for its
indirect determination down to 0.019ppm F – .This concentration can be lowered even
more than that obtained with fluoride ion selective electrode if standard addition method
was used. The recovery of F – ion was between 105-95%, with C.V. 2%. This method
was .used for the determination of F – ion in water and toothpaste and compared with
the results obtained with fluoride ion-selective electrode using statistical treatments.
Keywords: The rather old and well known Fe(III)-thiocyanate system has been restudied. The
stepwise mole ratio complexation between them has been carefully confirmed. A
wavelength shift from 460 t0 480 nm has been observed by increasing SCN- ion
concentration and remained constant at 480nm.where Fe(III): SCN- was 1:6. An
improvement in the problem of stability of the complex has also been achieved by
creating an oxidizing medium using 9.5x10-4 M KMnO4 , to prevent the inner redox
reaction between SCN- and CNS-. The stability has been improved from zero time to
about 47 mins. Total iron has been determined in water and drugs down to 0.06ppm Fe3+
with r2 = 0.9997 ,recovery of 99.1-102% and precision of 0.13%. A hypsochromic
shift from 480 to 410 nm. caused by the effect of fluoride ion was exploited for its
indirect determination down to 0.019ppm F – .This concentration can be lowered even
more than that obtained with fluoride ion selective electrode if standard addition method
was used. The recovery of F – ion was between 105-95%, with C.V. 2%. This method
was .used for the determination of F – ion in water and toothpaste and compared with
the results obtained with fluoride ion-selective electrode using statistical treatments.